Assembly molding process for electrical elements



May 26, 1959 FlGQl. 9

B. L. SNAVELY ASSEMBLY MOLDING PROCESS FOR ELECTRICAL ELEMENTS OriginalFiled July 7, 1949 2 Sheets-Sheet 1 39 ,3 I, 35 2o 4 as IH ll 40 37 I3nnuqw mum: 12 INVENTOR 4 l7 '8 22b 220 B. SNAVELY ATTRNEYS.

" y 1959 B. L. SNAVELY 2,887,763

' ASSEMBLY MOLDING PROCESS FOR ELECTRICAL ELEMENTS Original Filed July7, 1949 2 Sheets-Sheet 2 v INVENTOR. 45 48 B. L. SN

United States Patent C) I ASSEMBLY MOLDING PROCESS FOR ELECTRICALELEMENTS Benjamin L, Snavely, Takoma Park, Md.

Original application July 7,' 1949, Serial No. 103,501, now Patent No.2,745,083, dated May 8, 1958. Divided and this application July 29,1955, Serial No.

525,406 v H i t Claims. (Cl. 29- 1ss.s

(Granted under Title 35, U.S. Code (1952), see. 266) The inventiondescribed herein may be manufactured and used by or for the Governmentof the United States of America for governmental purposes without thepayment of any royalties thereon or therefor.

This invention relates to assembly molding processes for electricalelements and more particularly pertainsto methods of. assemblingelectromagnetic transducer arrangements of thetype disclosed in mycopending application Serial No. 103,501, filed July 7, 1949, now U.S.Patent No. 2,745,083, of which this is a divisional application.

More specifically, the invention is directed to methods of assembling anelectromagnet within a suitable apertured supporting structure byenergizing the'electromagnet so as to maintain it in a fixedpredetermined position within the aperture of the supporting structurewhile pouring a dimensionally stable mold about the electromagnet insuch a manner that the electromagnet is rigidly retained within theaperture andso encased by the-mold as to have a planar face thereofexposed'for electrica communication with an armature.

Ruggedness in construction is of particular importance in transducerdevices since these devices are often handled by unskilled persons whoare unaware of the delicacy of adjustment so necessary to maintaincontinued accuracy of these instruments. Furthermore, due to-the designof prior arrangements of devices of this character,

diificulty has been encountered in manufacturing these devices with thesmall tolerances that are required. Heretofore, it has been necessarytoprovide shims for adjusting the air gaps of the individual units toobtain satisfactory operating characteristics.

In order to eliminate the difiiculties in the manufacture of devices ofthis nature and to provide devices having extremely small manufacturingtolerances, the present invention provides new methods and means ofassembly and construction which will not only find application in thehydrophones described herein for purposes of illustrating the methods ofthe invention but which will also find general application in theconstruction of other types of transducers and in other kinds ofelectrical-instruments. Inparticular, theinvention provides novel ICCthe supporting structure to fixedly support the assembly within theconfines of the hollow section of the supporting structure.

-Wi-th the foregoing in mind, it is an important object ofthe presentinvention to provide methods of general application for mountingsensitive electrical unitswhich must be protected from shock and at thesame time maintained in fixed spatial relationship with associatedelements,

- Anotherobject is to provide new and improved methods ofmanufacturingsensitive electrical units which are of rugged and shock-resistantconstruction.

It is a further object of the invention to provide methods and means forconstructing a transducer, particularly of'the hydrophone type, whichwill result in small manufacturing tolerances, especially inestablishment of the air gap between the armature and the core and coilassembly.

. A significant object of theinvention is the provision of methods formounting sensitive electrical components by means of a dielectricencasement for reducing eddy current effects while simultaneouslymaintaining the associated components in fixed spatial relationship.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detttiledldescription when considered inconnection with the accompanying drawings in which like referencenumerals designate like parts throughout the figures thereof andwherein:

Fig. '1 is a sectional view of one form of transducer having thesensitive electrical components thereof mounted in accordance with theteachings of the invention;

Fig.2 illustrates one method of the invention employed for supporting acore and coil assembly in the supporting structure of Fig. 1; and

Fig, 3 is a center section of another form of transducer havingthe-sensitive electrical elements thereof mounted in. accordance withanother method of the invention.

Referring now to Fig. 1, wherein is shown a hydrophone employing theassembly teachings of the invention, the numeral 4 refers to a backingplate to which the diaphragm 5 is attached. The plate 4 is of an annularcon: struction and has mounted within its centrally located aperture 35the core and coil assembly 22. The backing plate 4'is welded to thefront of a cylindrical casing 3 which houses electrical componentswithin a water-tight methods .01": construction for accuratelyestablishing the cally, the invention contemplates methods ofmagnetizing the core and coil assembly so as to rigidly maintain it in apredetermined position by magnetic traction within ahollow supportingstructure while thecore and coil assemblyis beingencased within a pouredcast-of plaster 9f Paris whi h, w raha d n digr siq y. tater-leeks w hchamber. 'A circular closure plate 6 seals the rear portioncf casing 3by means of bolts 62, and a cable 9 is led into the casing 3 through apacking gland formed in a boss 8.v Intermediate backing plate 4 andclosure plate 6-, a;bulkhead plate 26 is provided which divides theinterior of the hydrophone into two water-tight compartments and whichsupports electrical components, such as condenser 33 and resistor 34,thereby protecting the electrical components in ,the front compartmentfrom damage in case water enters the hydrophone through cable 9 and itssurrounding gaskets.

' Referring now more particularly to the coil and core 22 and to themanner of .its assembly within its supporting elements, it will'be seenthat the backing plate 4 is provided, with a centrally located aperture35. A shoulder 36 is formed-within. the aperture 35, and a hollowcylindrical auxiliary supporting member 24 is provided with a flange 37which is seated on and supported by shoulder "36. Bolts 138 securecylindrical member24tto the backing plate 4. A pin 39, fixed to thebacking plate, passes through a hole in the flange 37 and serves todijs-. pose-the coreand coil in a predetermined angular position within.its supporting elements. The core and coil ans1. ti s.. .n n a esupported nand r wndeq by a mass of molded plastic dielectric material25 which rigidly supports the core and coil assembly within thecylindrical member 24 and insulates it from its surrounding metallicsupporting members. Preferably an annular rib 40 is formed within thecylindrical member 24 to more effectively anchor the plastic material25.

Diaphragm 5 is made up of a central vibrating portion 14 and aperipheral annular section 13 which is thicker than the central portion14 and which supports the diaphragm on the flat outer sealing surface ofthe backing plate 4. The central vibrating portion 14 of the diaphragmis slightly thickened at its outer edges, as at 15, in order to preventthe central portion 14 from breaking away from the thick supportingannulus 13 when the diaphragm is subjected to a very large deflection. Aboss 16 is formed on the interior face of the diaphragm at the centralportion thereof. Cemented to this boss is a disc-shaped permalloyarmature 17 which is protected from damage by a Bakelite resin guardring 18. A metal gasket 21 between the sealing surfaces of the diaphragmand the backing plate provides a watertight seal, and at the same timespaces the armature 17 and the core and coil assembly 22 a predetermineddistance from each other. The assembly of the core and coil within itssupporting elements forms an important feature of the invention.

The method of manufacturing this assembly, in accordance with thepresent invention, will now be described and may be understood morereadily by reference to Fig. 2. First of all, the flat peripheralsealing surfaces of the diaphragm and the outer face of the armature 17are simultaneously ground flat and coplanar with one another. Next, thehollow cylindrical member 24 is bolted in place on the backing plate andthe sealing surfaces of the backing plate and the circular lip 41 of thecylindrical member 24 are simultaneously ground flat and so as to becoplanar. The cylindrical member 24 is then removed from the backingplate and clamped $91 to flat steel plate 42. Following this, the coreand coil assembly 22 including core 22b which has its face groundperfectly flat is positioned within the cylindrical member 24 in faceadjacency with the surface of the steel plate as shown in Fig. 2, andprecisely centered therein by means of a jig (not shown). A current ofone or two amperes is then passed through the coil 22a through leads 43,thus cifectively anchoring the core and coil in a fixed relation to thecylindrical member 24 by means of magnetic traction. Following this, thejig is removed and a suitable liquid dielectric material of a characterproviding dimensional stability after hardening is cast around the coreand coil filling the interior of the cylindrical member 24. Before thedielectric material hardens, terminals 23 are embedded in its surface. Asatisfactory dielectric material for casting around the coil and coreassembly is a plaster of Paris composition having resinous strengtheningbinder. This casting composition has been found to have excellentdielectric properties and also to provide a mechanically rugged andshock proof support for the core and coil assembly which thereaftermaintains a constant position of this assembly in the cylindricalmember. It will be readily apparent that, when the dielectric mass 25has hardened and the cylindrical member 24 is removed from thesupporting surface 42, the outer surfaces of the core 22b will becoplanar with the circular lip 41. When this assembly is bolted in placeon the backing plate, the peripheral sealing surfaces of the backingplate, the

circular lip 41, and the outer surfaces of the core 22b I bled on thebacking plate without a gasket therebetween, the outer face of thearmature would directly abut the outer face of the core 22b. An air gapof any desired size between the face of the armature and the face of thecore may be established by inserting a gasket of proper thicknessbetween the sealing surfaces of the diaphragm and the backing plate. Thecharacteristics and elficiency of the transducer of the invention dependvery heavily on the accuracy with which the air gap between the armatureand the core is established. The construction described above permitsthis air gap to be established of any predetermined size depending onthe choice of the thickness of the gasket, and with an accuracy limitedonly by the accuracy with which the coplanar surfaces are ground.

Referring now to Fig. 3, wherein is shown another diaphragm arrangementin a hydrophone, there is provided a diaphragm 45 having a thickperipheral portion 54 which is bolted to the fiat peripheral portion ofbacking plate 46. An armature 47, similar in all respects to thearmature 17 described above, is afiixed to the center of the perfectlyflat interior face of the diaphragm. The outer surface of the diaphragm,opposite the armature 47, is thickened as at 48. When the diaphragm issubjected to extreme deflections, the thickened center portion of thediaphragm will tend to remain flat, and this will prevent stressesbetween the armature and the diaphragm which might break them apart.

The backing plate 46 is provided with a centrally located aperture 49 inwhich a coil and core assembly 22, similar in all respects to thatdescribed above, is rigidly fixed by a mass of molded plastic dielectric50 which supports assembly 22 and the terminals 51 in the same manner ascasting 25 above. The core and coil assembly 22 is directly opposite thearmature and is spaced therefrom by an air gap of predetermined size. Itis to be noted that the face of the core and coil assembly is notcoplanar with the peripheral sealing surfaces of the backing plate as isthe case in Fig. l and there is no gasket between the backing plate ofthe diaphragm to establish the air gap between the armature and the coreand coil assembly as in the arrangement of Fig. 1.

The method of mounting the core and coil assembly of Fig. 3 is similarto the method described in connection with the hydrophone of Fig. 1 witha slight variation in procedure in order to compensate for the recessedcore and coil assembly and to establish the air gap with the desiredaccuracy.

In order to establish the air gap and to fixedly recess the core andcoil assembly, the following procedure is followed. The diaphragm 45with the armature 47 affixed thereto is bolted to the backing plate 46.The diaphragm and backing plate are then laid in a horizontal positionwith the armature 47 facing upward. A circular metallic disc of diameterjust slightly smaller than the hole in the back plate and of thicknessequal to the required air gap is then laid on the armature, and the coreand coil assembly is placed in position against the disc. The core andcoil assembly is centered with a suitable jig and held in place bymagnetic traction as previously explained. A plastic dielectric is thencast around the core and coil assembly filling the aperture in thebacking plate and is then allowed to harden. The diaphragm is thendisassembled from the backing plate and the circular spacing discremoved. Upon reassembling the hydrophone, an air gap of the desiredmagnitude will have been established with great accuracy.

The advantages of the above described method and means for mounting acore and coil within its supporting members are many. The castdielectric material 25 and 50 which encases the coil and core assembliesin Figs. 1 and 3, respectively, prevent any displacement of the core andcoil with reference to the armature or its surrounding supportingmembers. The core and coil of Fig. 1 is held in strict coplanarrelationship with the sealing/surfaces of the backing plate andtherefore is held'strictly parallel to the armature. In Fig. 3, the coreand coil are recessed within the backing plate a distance equal to thedesired air gap. The dielectric material in addition prevents the flowof eddy currents which might be set up in the surrounding metallic,supporting elements."v In a simple and rapid manner the core and coil isaccurately centered within the member 24 and the outer surface of thecore aligned in perfect coplanar relationship with the annular lip 41 inthe arrangement of Fig. l and perfectly recessed in the arrangement ofFig; 3. While the dielectric composition 25 and 50 are cast orotherwiseformed around the corel-and coil and within the cylindrical member 24and backing plate 46, respectively, the core and coil is rigidly held inthis predetermined position by means of magnetic traction. Thus there isno possibility of displacement of the core and coil assembly whileplastic material is formed, around it. The foregoing construction andmethod of assembly of th'ecore and coil element within its supportingmembersmay obviously be applied to the construction and assemblyof anydesired type of transducer element where high accuracy and ruggedness ofconstruction are particularly desirable. t

J Obviously many modifications and variations of the presentinventionare possible in the light of the above teachings. ,It is therefore to beunderstood that within the. scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed as new and desired to be secured, by Letters Patent ofthe United States is:

l. The method of mounting a magnetizable electrical assembly in apredetermined position within the concavity of a supporting member, saidelectrical assmebly including an electrically conductive path terminatedby a pair of terminal elements: said method comprising the steps ofsupporting said member on a planar magnetizable surface, positioningsaid assembly within the concavity of said member in said predeterminedposition and supported in said position by said magnetic surface,magnetizing said assembly by applying electrical potential across saidpair of terminal elements to pass current through said conductive pathwhereby said assembly is retained in said predetermined position withinsaid concavity by magnetic traction with said magnetizable surface,pouring a hardenable fluid mixture of plastic material into saidconcavity and around said assembly, whereby said assembly is fixedlysupported within said concavity uponvhardening of said plastic material,and embedding a portion, of each. of said terminal "elements in saidplastic material prior .to the hardening thereof. 2. The method ofmounting a magnetizable electrical assembly in a predetermined positionwithin a supporting member .having .an aperture in a flat facethereof,,.said electrical assembly including an electrically conductivepath terminated by a pair of terminal elements: said method comprisingthe steps of supporting said flat face in face-adjacency on a flatmagnetizable surface, positioning said assembly within the aperture insaid member in said predetermined position and in abutting faceadjacencyto said flat magnetizable surface, magnetizing said assembly by applyingelectrical potential 'cross said pair of terminal elements to passcurrent through said conductive path whereby said assembly is held insaid predetermined position by magnetic traction with said magnetizablesurface, pouring a hardenable fluid dielectric into said aperture andaround said assembly, whereby said assembly is insulatably supported insaid apertured member upon hardening of said dielectric, and embedding aportion of each of said terminal elements in said dielectric materialprior to the hardening thereof. 3. The method of mounting a magnetizableelectrical assembly in a predetermined position within a supportingmember having an aperture in a flat face thereof, said electricalassembly including an electrically conductive sembly is held in saidpredetermined position by magnetic traction with said spacing memberpouring a hardenable'fiuid mixture of dielectric material into saidaperture and around said 'assembly,*whereby said assembly is rigidlysupported in and insulated from said apertured member upon hardening ofsaid material and embedding a portion of each of said terminal elementsin said dielectric material prior to the hardening thereof.

4. The method of mounting a magnetizable electrical assembly in apredetermined position within a supporting member havingwan; aperture ina flat face thereof and simultaneouslyv establishing an air gap betweensaid assembly and an armature. coacting therewith, said electricalassembly including an electrically conductive path terminated by a pairof terminal elements: said method comprising the steps of detachablymounting said flat face in abutting face adjacency on the fiat portionof a supporting framework having said armature affixed thereto andpositioned thereon to extend Within said aperture, placing a flatmagnetizable spacing member on said arma: ture, supporting a flatsurface of said assembly on said flat spacing member in face-adjacencytherewith, magnetizing said assembly by applying an electrical potentialacross said terminal elements to pass current through said conductivepath whereby said assembly is held in said predetermined position bymagnetic tractionwith said spacing member, pouring a hardenable slurryof dielectric material into said aperture and around said assembly,embedding a portion of each of said terminal elements in said slurry,permitting said slurry to harden, separating said supporting member fromsaid supporting framework, removing said flat spacing member, andsecurely' remounting said supporting member on said frame,- work wherebysaid assembly is supported in and insulated from said supporting memberand spaced a predetermined distance from saidarrnature in accordancewith the thickness of said flat spacing member.

5. The method of mounting a magnetizable electrical assembly in apredetermined position within the con? cavity of a supporting structure,said electrical assembly including an electrically conductive pathterminated by a pair. of terminal elements: said method comprising thesteps of supporting said assembly within said concavity and in saidpredetermined position by means of:a magnetizablemember, magnetizingsaid assembly by applying an electrical potential across said terminalsto pass current through said conductive path whereby said assembly isheld in said predetermined position within said concavity by magnetictraction with said magnetizable member, casting a hardenable fluidplastic mixture around said assembly, whereby said assembly is fixedlysupported within said concavity upon hardening of said mixture andembedding a portion of each of said terminal elements in said mixtureprior to the hardening thereof.

6. A casting method of rigidly and insulatably encasing a magnetizableelectrical unit within a hollow housing structure, said unit includingan electrically conductive path terminated by a pair of terminalelements: said method comprising the steps of assembling the housingstructure on a supporting assembly of which at least a portion thereofis magnetizable, supporting the electrical unit within the hollowhousing structure by means of said assembly and positioned in abuttingrelation with 7 the magnetizable portion thereof, applying an electricalpotential across said pair of terminals to pass electric current throughsaid conductive path thereby to magnetically anchor the electrical uniton the magnetizable portion of said assembly, casting a hardenableliquid dielectric within said housing structure and around saidelectrical unit whereby said unit is rigidly and insulatably retained bysaid housing structure upon hardening of said dielectric, and embeddinga portion of each of said terminals in said dielectric prior to thehardening thereof.

7. The method of mounting a magnetizable electrical unit in apredetermined position within a supporting member having a referenceface of predetermined configuration with a bore entering said face andextending at least part way into said supporting member, an irregularconcavity forming a portion of said bore, and said electrical unitincluding an electrically conductive path terminated by a pair ofterminal elements: said method comprising the steps of assembling saidsupporting member on a structural assembly with said reference face inabutting engagement with a similarly configured face of said structuralassembly of which'at least a portion is magnetizable, supporting theelectrical unit in said predetermined position within said irregularconcavity by means of said magnetizable portion of said structuralassembly, applying electrical potential across said pair of terminals topass electric current through said conductive path thereby tomagnetically anchor the electrical unit on the magnetizable portion ofsaid assembly, filling said concavity with a hardenable liquid materialof a character providing dimensional stability after hardening,embedding a portion of each of said terminal elements in said material,and allowing said material to harden whereby the irregularities of saidconcavity rigidly interlock said hardened material to thereby fixedlysupport said electrical unit within said concavity in said predeterminedposition with said terminal elements having exposed portions forelectrical connection.

8. In the method of claim 7, the hardening step being promoted by theutilization of a slurry of plaster of Paris as the hardenable liquidmaterial.

9. The method of rigidly mounting an electromagnet formed by a core witha coil terminated by a pair of terminal elements, in a predeterminedposition within a casing having a reference face of predeterminedconfiguration with a bore entering said face and extending at least partway into said casing, an irregular concavity forming a portion of saidbore, comprising the steps of supporting said casing on a magnetizablemember with said reference face resting on a similarly configured faceof said member, positioning the electromagnet within said concavity witha face of the electromagnet resting on a similarly configured face ofsaid member, magnetizing said electromagnet by applying an electricalpotential across said terminals to pass current through said coilwhereby said electromagnet is securely retained within 0 said concavityby magnetic traction with said member, filling said concavity with aquick-drying liquid dielectric of a character providing dimensionalstability after hardening, embedding a portion of each of said terminalelements in said dielectric, and allowing said liquid dielectric to dryand harde'n whereby the irregularities of said concavity rigidlyinterlock said hardened material to thereby fixedly support saidelectromagnet within said concavity with said terminal elements havingexposed portions for electrical connection.

10. The method of rigidly mounting an electromagnet formed by a corewith a coil terminating in a pair of terminal elements, in apredetermined position within a casing having a reference face ofpredetermined configuration with a bore entering said face and extendingat least part way into said casing, an irregular concavity forming aportion of said bore, and simultaneously establishing an air gap betweensaid electromagnet and an armature operatively associated therewithcomprising the steps of detachably assembling said reference face ofsaid casing on a similarly configured face of a supporting frameworkhaving said armature affixed thereto and positioned to extend into saidconcavity, placing a flat magnetizable spacing member on said armature,supporting a flat surface of said electromagnet on said spacing memberin said predetermined position within said concavity, magnetizing saidelectromagnet by applying electrical potential across said pair ofterminals to pass current through said coil to thereby retain saidelectromagnet in said predetermined position by magnetic traction withsaid spacing member, filling said concavity with a hardenable slurry ofdielectric material, embedding a portion of each of said terminalelements in said slurry, allowing said materials to harden wherebytheirregularities of said concavity rigidly interlock said hardenedmaterial to thereby fixedly support said electromagnet in saidpredetermined position within said concavity, disassemblying said casingand supporting framework, removing said spacing member, and securelyreassembling said casing and framework whereby said electromagnet issupported in and insulated from said casing and spaced a predetermineddistance from said armature in accordance with the thickness of saidspacing member.

References Cited in the file of this patent UNITED STATES PATENTS

